Developer Insights: The Secret to Scale in VR

December 01, 2016 by Crytek

You might think that you see with your eyes, but technically, that’s not true. You see with your brain, and your eyes are the user interface between your brain and the world. It follows that how you see the world is dependent on how your UI—in this case, your eyes—are positioned. Adjust that positioning, and you can adjust a person’s perception of the world.

While you can’t just adjust the position of your eyes in real life, developers can artificially do so in VR. And changing the positioning of your eyes, or in this case the perceived positioning of your eyes, allows them to manipulate a player’s sense of scale in their virtual worlds.

One very important factor in human perception of scale is the distance between your eyes, something known as inter-pupillary distance or IPD. When VR developers artificially alter your IPD, they can alter a player’s perception of their height and the relative size of any creatures they encounter. One small sleight of hand—or should we say sleight of eye—and a virtual dinosaur can go from cute little creature to monstrous giant.

“Because your brain knows about how tall your body is, you can easily experience sensory conflict in VR and that can really mess up your sense of scale,” explains Animation Programmer Ali Helmy. “Instead of accepting your in-game eye-level as your own height, you end up feeling like you are partially buried, or floating in the air. During our Back to Dinosaur Island 1 demo’s development, we wanted players to encounter an enormous dinosaur. But in the first iterations of that demo, you didn’t feel like you were small and the dinosaur was big. You felt like you were your usual size, the dinosaur was maybe the size of a big cow, and your body was buried in the ground to your chest. Weird, right?”

But thanks to some unrelated research undertaken at the Goethe University in Frankfurt, the VR team realized that IPD was the key to the sense of scale in VR.

“They were doing psychology studies, and they found that the brain uses this focal distance (your IPD) as its measure for everything. Dario and the rendering wizards realized that because we had the offset of the cameras at 6.5 centimeters—which is the average distance between an adult’s eyes—players were assuming that their bodies were the same size as they are in real life.

“So we scaled down the IPD. If you make that distance smaller, your brain still assumes it is 6.5 centimeters, and that scales up your perception of the world. So suddenly that dinosaur feels huge. And we didn’t have to change anything. No one scaled anything in the map, nothing.”

Instead of the usual 6.5 cm IPD, players were given a 2 cm IPD—basically, a child’s perspective. Players were able to accept this as their own height and the rest of the world seemed enormous in comparison.

“That is one of the very weird things that came out of our research. We realized that the focal distance between the eyes plays a huge roll in your perception of the world. And that’s why children don’t feel like they are small, they feel like they’re regular-sized and everybody else is over-sized. Rescale players’ perception of themselves and the rest of the world scales with them. That was a very cool discovery.”

We learned how to hack scale in VR, and we learned it from research done in another field. The takeaway is clear: read widely, try everything, and keep only the best solutions. In the early days of VR, pioneering developers will be the ones to shape the medium’s foundations.